N(n&#39;-maleimidomethyl)citraconimide

ABSTRACT

A METHOD IS PROVIDED FOR MAKING A VARIETY OF N,N&#39;&#39;METHYLENE BISMALEIMIDES BY INTRODUCING BORON TRIFLUORIDE INTO A MALEIMIDE MIXTURE CONTAINING EITHER PARAFORMALDEHYDE OR METHANOL MALEIMIDE. THE N,N&#39;&#39;-METHYLENE BISMALEIMIDES MADE BY THE SUBJECT METHOD CAN BE SYMMETRICAL OR UNSYMMETRICAL AND ARE USEFUL FOR MAKING POLYIMIDES.

United States Patent 3,833,609 N(N'-MALEIMIDQ THYL) CITRACONIMIDE John R. Ladd, Balls ton Lake, N.Y., assignor to General 1 El'ec'tric'Company,"Schenectady, N.Y.

No' DrawingJ-Filed Apr-.21, 1972, Ser. No. 246,287

151260-i-i-326z26 4 1 Claim ABSTRACT, 0F. DISCLOSURE y if making a variety of N,N'- jiithylene biismal'eimides by int'or ducing boron trifluoride into a maleiriiide mixture containing either paraforrnalde- "br metharibl maleiniide. The N,N'-methylene bisimide's made by the subject method can be symmerfieai or unsymmetrical-j and are useful for making polyimides i p ej jpre'sent invention relates to a method for making 1'N,I}l' methylene bismaleimides and products made there- J flOlll More particularly,f;the present invention relates to 1 se fja' boron trifluoride as a catalyst in a maleimide e of paraforrifald ehyde or'a N-methanol maleimide. "*The inal'ei'mide's provided by the" present invention are selected from the class consisting of symmetrical N,N'- methylene bismaleimides of the'foriiiu'la,

unsymmetrical Nil me thylene bismaleimides,

(a) a mixture of formaldehyde, and about two moles,

per mole of formaldehyde of a maleimide of the formula,

Ito-ii u NH, and R C (b) :a mixture of substantially equal moles of said maleimide of (a) and an N-methanolmaleimide of the formula,

0 INC- and (2) recovering an N,N'-methy1ene bismaleimide from the mixture of (1), where 'R, R R and R are as previously defined.

Included by the symmetrical bismaleimides of formula 1 are for example, N,N-methylenebisdichloromaleimide, N,N methylenebiscitraconimide, N,N' --methy-lenebis chloromaleimide. There are included by the unsymmetrical bismaleimides of formula 2, N-(citraconimidomethyl) maleimide, N (maleimidomethyl)chloromaleimide, N- (citraconimidomethyl)dichloromaleimide.

-In the practice of the invention, the symmetrical bismaleimides of formula 1 can be prepared by initially dissolving maleimide in an organic solvent, such as for example, methylene chloride, chloroform, etc., and adding paraformaldehyde to the resulting solution in an effective amount. An effective amount of paraformaldehyde is any amount which is at least sufficient to provide one half mole of formaldehyde, per mole of maleimide. Boron trifluoride is then introduced into the mixture at a rate which does not allow for any excess to escape from the reaction mixture. As soon as the mixture is saturated with boron trifluoride, excess solvent can be decanted from the mixture, followed by the addition of a solvent, such as methanol to effect the precipitation of product. Recovery of the product and its purification can be effected by standard techniques, such as by filtration, recrystallization in boiling aliphatic alcohol, etc.

Alternatively, if it is.desired to make unsymmetrical methylene bismaleimide, boron trifluoride can be introduced into an organic solvent solution of substantially equal molar amountsof themaleimide and the methanol maleimide. The precipitation and therecovery of the resulting methylene bismaleimide can then proceed in accordance with the previously described procedure.

During the introduction of the boron trifluoride tothe above described mixture, stirring or agitation by other known means can be employed to facilitate the interaction of the various ingredients of the mixture. Temperatures in the range of between 0 C. to 60 C(can be employed. It has been found that an exothermic reaction results upon the introduction of boron trifluoride, which can require the use of an external cooling means, such as an ice bath.

It has been found that the 'rfinal product is generally a crystalline material, which has a relatively sharp melting point. However, in instances where unsymmetrical methylene bismaleimides are made, a mixture of up to 3 methylene bismaleimides can occur, which may interfere with the recovery of a pure compound. Resolution of the mixture can be facilitated by the use of such analytical means as chromotography, etc.

The methylene bismaleimides of the present invention can be employed in combination with other reagents, such as arylene diamines or polyalkylene diamines to make a variety of polyimides, such as shown by Kovacic Patent 2,818,405 and Grundschober et a1. Patent 3,380,964 and Sambeth et a1. Patent 3,406,148, etc.

In order that those skilled in the art will be better able to practice the invention, the following examples are given by way of illustration and not by way of limitation. All parts are by weight.

EXAMPLE 1 Boron trifluoride was introduced into a mixture of 9.71 parts of maleimide, 12.7 par-ts of N-methanol maleimide andv about-500 parts of methylene chloride, while the resulting mixture was stirred. The mixture became exothermic and an ice bath was applied to maintain the temperature of the mixture below about 30 C. Boron trifluoride was introduced at a rate so little or no excess escaped from the reaction mixture. There was obtained a gummy precipitate. The methylene chloride was then decanted from the mixture and there was added to the resulting product, about 100 parts of methanol with cooling. There was obtained 15 parts of a white solid. It was recrystallized from about 250 par-ts of boiling aqueous ethyl alcohol to produce a crystalline product having a faint yellow color and a melting point of 171 C. Based on method of preparation the product was N,N-bismale imide.

When equal molar amounts of N,N'-methylenebisma-leimide and methylene dian iline heated together as a 10 percent solution in dimethyl-formamide at 150-155" for three hours, a powdered resin was for-med which was precipitated by addition of the reaction mixture in methyl alcohol. Upon fusing the powdered resin at 350 C., it was found to form a film having good dielectric properties.

EXAMPLE 2 EXAMPLE 3 'Boron trifluoride was slowly passed into a mixture of 0.2 parts of citraconimide and 0.03 parts of paraformaldehyde dissolved in about 5 parts of methylene chloride. After the mixture had been saturated with boron trifluoride, the methylene chloride was decanted yielding a gummy product. The gummy product was recrystallized from methanol and a crystalline material was obtained. Based on method of preparation, the crystalline product was N,N'-methylene biscitr-aconimide having the formula,

A mixture of about .25 parts of poly sopre e diaiiiine, 0.176 parts of diethylene triamine' and aboutteltparts of N,N'-methylene biscitr'aco'nimidefis milledand cast into a thin film. The film is cured at about 'il50325(2.="for$15 minutes. An elastomeris-obtained, exhibiting valuable insulating properties..-.-.-.w A

E 1 5 3 15,? 1 Boron trifluoride was-slowly-introduced:intoa {9 of 0.13 parts of N-methanoLm-aleimide an lv lpartof citraconirnide in about-'5 parts p fsmethy h ide,

Following the procedure of Example 3, the was obtaind a crude crystalline material. Based on. method of prepar 7 tion, the product was =N(N'-maleimidomethyl)citraco imide. 1

Although the above examples are limitedttopnlya few of the very many N,Nf-metliylene":hismale ides, can be made in the .pr acticelof the present in should be understood thattliepresent'invention is d M to a much broader class of iboth.symmetricalfl dflf bisf maleimides of formula .1, ana ;un ymm' icaLMN -bismaleimides of formula 2. i f I What I claim as desii; Patent of the United States is': i

1. The compound N(N malein idomethyncitracon; imide.

References "Cited UNITED STATES @TENTS 2,850,351 9/1958 Mooreft "a1. 2' 8--127.6 3,018,290 1/ 1962 Sauers, et al.-"" 260-6263 3,129,225 4/1964 Shapiro 2 247.2

OTHER REFERENCES 7 Smets, et -al., Ger. Oflen. 1, 963, 731 3 September Chemical Abstract 73': 10434311 197025 DONALD G. DAUS, PrimaryExaminer R. D. MCCLO UD, Assistant Examiner 

